package com.morder.util;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Scroller;

public class MyScrollLayout extends ViewGroup {

  private static final String TAG = "ScrollLayout";

  private VelocityTracker mVelocityTracker; // 用于判断甩动手势

  private static final int SNAP_VELOCITY = 600;

  private Scroller mScroller; // 滑动控制

  private int mCurScreen;

  private int mDefaultScreen = 0;

  private float mLastMotionX;

  private OnViewChangeListener mOnViewChangeListener;

  public MyScrollLayout(Context context) {
    super(context);
    init(context);
  }

  public MyScrollLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
    init(context);
  }

  public MyScrollLayout(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    init(context);
  }

  private void init(Context context) {
    mCurScreen = mDefaultScreen;

    mScroller = new Scroller(context);
  }

  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
    if (changed) {
      int childLeft = 0;
      final int childCount = getChildCount();

      for (int i = 0; i < childCount; i++) {
        final View childView = getChildAt(i);
        if (childView.getVisibility() != View.GONE) {
          final int childWidth = childView.getMeasuredWidth();
          childView.layout(childLeft, 0, childLeft + childWidth, childView.getMeasuredHeight());
          childLeft += childWidth;
        }
      }
    }
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);

    final int width = MeasureSpec.getSize(widthMeasureSpec);

    final int count = getChildCount();
    for (int i = 0; i < count; i++) {
      getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
    }
    scrollTo(mCurScreen * width, 0);
  }

  public void snapToDestination() {
    final int screenWidth = getWidth();

    final int destScreen = (getScrollX() + screenWidth / 2) / screenWidth;
    snapToScreen(destScreen);
  }

  public void snapToScreen(int whichScreen) {

    // get the valid layout page
    whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
    if (getScrollX() != (whichScreen * getWidth())) {

      final int delta = whichScreen * getWidth() - getScrollX();

      mScroller.startScroll(getScrollX(), 0, delta, 0, Math.abs(delta) * 2);

      mCurScreen = whichScreen;
      invalidate(); // Redraw the layout

      if (mOnViewChangeListener != null) {
        mOnViewChangeListener.OnViewChange(mCurScreen);
      }
    }
  }

  @Override
  public void computeScroll() {
    if (mScroller.computeScrollOffset()) {
      scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
      postInvalidate();
    }
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    final int action = event.getAction();
    final float x = event.getX();

    switch (action) {
    case MotionEvent.ACTION_DOWN:

      Log.i("", "onTouchEvent  ACTION_DOWN");

      if (mVelocityTracker == null) {
        mVelocityTracker = VelocityTracker.obtain();
        mVelocityTracker.addMovement(event);
      }

      if (!mScroller.isFinished()) {
        mScroller.abortAnimation();
      }
      mLastMotionX = x;
      break;

    case MotionEvent.ACTION_MOVE:
      int deltaX = (int) (mLastMotionX - x);

      if (IsCanMove(deltaX)) {
        if (mVelocityTracker != null) {
          mVelocityTracker.addMovement(event);
        }

        mLastMotionX = x;

        scrollBy(deltaX, 0);
      }

      break;

    case MotionEvent.ACTION_UP:

      int velocityX = 0;
      if (mVelocityTracker != null) {
        mVelocityTracker.addMovement(event);
        mVelocityTracker.computeCurrentVelocity(1000);
        velocityX = (int) mVelocityTracker.getXVelocity();
      }

      if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {
        // Fling enough to move left
        Log.e(TAG, "snap left");
        snapToScreen(mCurScreen - 1);
      } else if (velocityX < -SNAP_VELOCITY && mCurScreen < getChildCount() - 1) {
        // Fling enough to move right
        Log.e(TAG, "snap right");
        snapToScreen(mCurScreen + 1);
      } else {
        snapToDestination();
      }

      if (mVelocityTracker != null) {
        mVelocityTracker.recycle();
        mVelocityTracker = null;
      }

      // mTouchState = TOUCH_STATE_REST;
      break;
    }

    return true;
  }

  private boolean IsCanMove(int deltaX) {
    if (getScrollX() <= 0 && deltaX < 0) {
      return false;
    }
    if (getScrollX() >= (getChildCount() - 1) * getWidth() && deltaX > 0) {
      return false;
    }
    return true;
  }

  public void SetOnViewChangeListener(OnViewChangeListener listener) {
    mOnViewChangeListener = listener;
  }

}
